Process of manufacturing loading coils



Patented Mar. 13, 1923.

UNITED STATES BENNETT H. JACKSON, OF NEW YORK,

COMPANY, INCORPORATED, OF NEW YORK,

YORK.

N. Y., ASSIGNOR TO WESTERN ELECTRIC N. Y., A CORPORATION OF NEW PROCESS OF MANUFACTURING LOADING COILS.

Nfo Drawing.

To aZZ whom it may concern Be it known that I, BENNETT H. JAcKsoN,

a citizen of the United States of America,

residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Processes of Manufacturing Loading Coils, of which the following is a full, clear, concise, and exact description.

This invention relates to inductance coils, such as'loading coils, for telephone lines. More particularly, it relates to a method of manufacturing cores for inductance coils whereby more uniform results are obtained in their electrical values.

For convenience this invention will be described in connection with inductance coils having iron dust cores of the type described in the Elmen Patent No. 1,286,965, of December 10, 1918, on magnet cores. The cores made in accordance with this patent are composed of finely divided electrolytic iron and insulating material of iron, which mixture has been subjected to enormous pressures to give the mixture at specific gravity approximately equal to that for undivided iron. One way in which the coil windings may be placed on a magnet core is described in detail in the Fondiller I0 Patent No. 1,212,755 of January 16, 1917.

It has been found, however, that such iron dust cores as they come from the press are sometimes not suited for immediate use in inductance coils or loading coils for the reason that their electrical values, such as their permeability, are not uniform and stable. It has also been found that the cores may he magnetized to a certain extent.

The unstable electrical properties of the cores is a particularly undesirable condition, especially when the cores are employed in loading coils, andthe like, where the manufacturing requirements are very rigid. Inaccuracies in the electrical values of loading coils lead to cross talk and other difiiculties when the coils are inserted in signaling lines, such as telephone lines.

According to this invention, the cores, preferably prior to placing the windings thereon, are subjected to a process which renders their electrical values, such as their permeability, stable and constant.

The cores, after coming from the press, are first den'iagnetized in any suitable way, such as by wrapping a few turns of wire Application filed March 20, 1920.

separating the particles Serial No. 367,440.

around the core and sending an alternatin current through the turns, gradually decreasing the current from a maximum value to zero.

After being demagnetized, the cores are then baked at a suitable temperature until their permeability values become stable and constant. A temperature from 200 to 300 F. for twelve hours will generally be sufficient, but in some cases it has been found desirable to prolong the heating for a period of sixty to seventy-two hours.

This baking of the cores corrects not only for the unstable electrical properties of the cores, which the cores possess prior to being demagnetized, but also corrects for any detrimental effects produced in the electrical properties of the cores n account of the demagnetization treatment. Experience has shown that the demagnetizing procem generally raises the permeability of the cores to a value somewhat higher than their normal values. a three to five per cent increase being the average. This increase, however, is substantially eliminated by the baking of the cores subsequent to the demagnetization.

Loading coils having cores which have been subjected to the above process are much more stable than coils having cores slightly magnetized, because experience has shown that the change in inductance of a coil caused by the application of comparatively small values of direct current, such as Morse telegraph currents, is much smaller in the case of a coil having a demagnetized core.

It is also preferable that the demagnetizing and heating treatments be applied to the (ore before the windings are placed thereon. One of the advantages gained thereby is the increased ease and certainty with which the coil windings can be adjusted to have a desired ratio of turns between inner and outer windings. This is particularly important in the case of phantom loading coils of the type described for example in the above mentioned Fondiller patent. In such a type of phantom coil, it is necessary to have a strict l-l ratio for some of the Winding sections thereon. Any departure from this ratio produces cross talk.

Another advantage in subjecting the coils to the process of this invention prior to the step of winding. is the fact that demagnetized cores may be kept in stock for an appreciable time before being wound, which results i n adeereglse in the electrical core losses and liliereffore assists in the manufacture of coils of minimum effective resistance which is the result desired.

\Vhat is claimed is:

1. The process f manufacturing a mag net core, whim comprises demagnetizing said core while the permeability of said wore i unstable, and baking said core until the iii-agnetic properties of said core have become stable.

2. The process of manufacturing a core for an inductance tOll, which comprises dcmagnetizing said core while the permeability of said core is unstable, and subsequently baking said core at a temperature of approximately 200 F.

3. The process of manutacturing an inductance coil having a core, which comprises forming said core demagnetizing said core, bakin said core at a. temperature of approximate y 200 F. for several hours, to over come the unstable magnetic values 0t said core due to its formation and demagnetization and subsequently placing the Wind- Pugs on said core.

4 The process atmanufacturing an in ductance (oil having a core. which comprises Forming said core, maintaining said core at a temperature substantially less than 5200 1C, demagnetizing said core and subsequent 1y halting said core at a temperature of approximately 200* F.

.5. The process of manufacturing an inductance coil having a core, which comprises forming said wort; slemagnetizinosaid core, baking said core until. the unstable magnetic properties of said core due to its formation and demagnetization have become substantially stable, and subsequently placing the windings on said core.

In witness whereof I hereunto subscribe my name this 17th day of March A. 11,1920.

BENNETT H. JACKSON. 

